diff --git a/makefile b/makefile
index 57f5efef..d6826150 100644
--- a/makefile
+++ b/makefile
@@ -176,6 +176,7 @@ ifeq ($(WIN32),)  #*nix Environments (&& cygwin)
     GCC_OPTIMIZERS_CMD = $(GCC) -v --help 2>&1
     GCC_WARNINGS_CMD = $(GCC) -v --help 2>&1
     LD_ELF = $(shell echo | $(GCC) -E -dM - | grep __ELF__)
+    INCPATH:=$(shell $(GCC) -x c -v -E /dev/null 2>&1 | grep -A 10 '> search starts here' | grep '^ ' | tr -d '\n')
     ifeq (Darwin,$(OSTYPE))
       OSNAME = OSX
       LIBEXT = dylib
@@ -276,7 +277,7 @@ ifeq ($(WIN32),)  #*nix Environments (&& cygwin)
             ifeq (X11R7,$(shell if $(TEST) -d /usr/X11R7/lib; then echo X11R7; fi))
               LIBPATH += /usr/X11R7/lib
               INCPATH += /usr/X11R7/include
-              OS_LDFLAGS += -L/X11R7/pkg/lib -R/usr/X11R7/lib
+              OS_LDFLAGS += -L/usr/X11R7/lib -R/usr/X11R7/lib
               OS_CCDEFS += -I/usr/X11R7/include
             endif
             ifeq (/usr/local/lib,$(findstring /usr/local/lib,$(LIBPATH)))
@@ -399,6 +400,12 @@ ifeq ($(WIN32),)  #*nix Environments (&& cygwin)
       OS_CCDEFS += -DHAVE_FNMATCH    
     endif
   endif
+  ifneq (,$(call find_include,sys/mman))
+    ifneq (,$(shell grep shm_open $(call find_include,sys/mman)))
+      OS_CCDEFS += -DHAVE_SHM_OPEN
+      $(info using mman: $(call find_include,sys/mman))
+    endif
+  endif
   ifneq (,$(VIDEO_USEFUL))
     ifneq (,$(call find_include,SDL2/SDL))
       ifneq (,$(call find_lib,SDL2))
diff --git a/sim_fio.c b/sim_fio.c
index 8381674f..16018cb4 100644
--- a/sim_fio.c
+++ b/sim_fio.c
@@ -459,6 +459,7 @@ struct SHMEM {
 
 t_stat sim_shmem_open (const char *name, size_t size, SHMEM **shmem, void **addr)
 {
+#ifdef HAVE_SHM_OPEN
 *shmem = (SHMEM *)calloc (1, sizeof(**shmem));
 
 *addr = NULL;
@@ -499,6 +500,9 @@ if ((*shmem)->shm_base == MAP_FAILED) {
     }
 *addr = (*shmem)->shm_base;
 return SCPE_OK;
+#else
+return SCPE_NOFNC;
+#endif
 }
 
 void sim_shmem_close (SHMEM *shmem)